Hot melt adhesives are widely used for various commercial applications such as product assembly and packaging, including cardboard case sealing and carton closing operations. Such hot melt adhesives are applied to a substrate while in its molten state and cooled to harden the adhesive layer.
Most commercially available hot melt adhesives require temperatures of 350° F. (177° C.) or greater to ensure complete melting of all the components and also to achieve a satisfactory application viscosity. While adhesive formulations that can be applied at temperatures below 300° F. (149° C.) can be prepared using low molecular weight components or a high wax content, application viscosity and adhesive properties suffer. While softer or more amorphous components may be added in order to improve adhesion, these components reduce the effective heat resistance.
The use of a hot melt adhesive with exceptionally high heat resistance and, in addition, good cold resistance is important in hot filled packaging applications, e.g., sealing and closing operations for cartons, cases or trays used for packaging molten cheese, yogurt or freshly baked goods, which are subsequently subjected to refrigeration or freezing.
There continues to be a need in the art for improved hot melt adhesives including hot melt adhesives that can be applied at low temperatures, and in particular hot melt adhesives possessing high heat resistance and good cold adhesion.